3 is the number of points received for a successful field goal in both American football and Canadian football.
4 is the number of characters in a canonical four-character idiom in Chinese.
20 is the number of questions in the popular party game Twenty Questions.
21 is the number of trump cards of the tarot deck if one does not consider The Fool to be a proper trump card.
37 is the normal human body temperature in degrees Celsius.
42 is the number of spots (or pips, circular patches or pits) on a pair of standard six-sided dice.
17 is the number of flames emanating from the grenade cap-badge of the Grenadier Guards.